Q&A: Understanding SOI and ROM in the APR-DRG system

Q: I need some help understanding severity of illness (SOI) and risk of mortality (ROM) as it’s my first encounter with APR-DRG factors that may affect reimbursement. First, how does one measure the SOI and ROM? Could you elaborate on how complications or comorbidities (CC) and major CCs (MCC) affect severity levels?

Second, what are the criteria for choosing the levels for SOI and ROM?

And finally, how do you classify the “sickest of the sick” patients when determining level 3 to 4 or level 4 to 3 for SOI and ROM?

A: There are many different types of DRGs used for inpatient payments. The payer determines which payment methodology they would like to use for reimbursement. Medicare uses Medicare Severity-Diagnostic Related Groups (MS-DRG), as do many private payers, but some may choose to use a modified reimbursement payment methodology.

The All Patient Refined DRG (APR-DRG) system was developed by 3M™, and in order to use this payment methodology, you need access to its APR-DRG grouper.

There are some key differences between MS-DRGs and APR-DRGs you need to understand as well. First, the APR-DRG system stratifies patients into two categories—SOI and ROM—each containing four groups ranging from minor (1), moderate (2), major (3), or extreme (4). The system also takes into account the patient’s age and sex. In the APR-DRG system, a condition will impact a patient’s SOI/ROM depending on what other conditions are present along with their demographic information (i.e., age and sex).

Each patient encounter is assigned one of more than 300 base APR-DRGs, and then assigned to one of the four levels I mentioned. Payment is typically based on the SOI value. A patient’s “severity” will depend on the number, nature, and interaction of complications and comorbidities, and the final APR-DRG assignment depends on the diagnoses/procedures reported on a claim.

Each diagnosis has its own SOI/ROM value. For example, a patient with a secondary diagnosis of uncomplicated diabetes mellitus (DM) would have a SOI score of minor, or 1, but DM with ketoacidosis would be major, or 3. Another example would be a patient with a secondary diagnosis of cardiac dysrhythmia with premature beats would be considered minor (1), while ventricular fibrillation would be extreme (4).

The Medicare (MS-DRG) system works differently. It stratifies patients based on the presence or absence of CCs or MCCs, and assigns them to one of more than 700 DRGs. These DRGs aren’t used in the APR-DRG system. I can’t emphasize enough, though, the importance of complete and accurate documentation, regardless of which system you are working with. That way, the coders are able to assign the appropriate codes for each encounter.

Editor’s Note: Sharme Brodie RN, CCDS, CDI education specialist and CDI Boot Camp instructor for HCPro in Middleton, Massachusetts, answered this question. For information, contact her at sbrodie@hcpro.com. For information regarding CDI Boot Camps offered by HCPro, visit www.hcprobootcamps.com/courses/10040/overview.